feat(prefer-expect-assertions): support requiring only if expect is used in a loop (#1013)

* feat(prefer-expect-assertions): support requiring only if `expect` is used in a loop

* test(prefer-expect-assertions): add cases for each

* chore(prefer-expect-assertions): add default value for `onlyFunctionsWithExpectInLoop` option

* test(prefer-expect-assertions): adjust some cases

* fix(prefer-expect-assertions): report expects in loops in functions in tests

* test(prefer-expect-assertions): format cases a bit

Author: G-Rath

docs/rules/prefer-expect-assertions.md

@@ -58,6 +58,16 @@ test('my test', () => {
 
 ## Options
 
+This rule can be configured to only check tests that match certain patterns that
+typically look like `expect` calls might be missed, such as in promises or
+loops.
+
+By default, none of these options are enabled meaning the rule checks _every_
+test for a call to either `expect.hasAssertions` or `expect.assertions`. If any
+of the options are enabled the rule checks any test that matches _at least one_
+of the patterns represented by the enabled options (think "OR" rather than
+"AND").
+
 #### `onlyFunctionsWithAsyncKeyword`
 
 When `true`, this rule will only warn for tests that use the `async` keyword.
@@ -97,3 +107,53 @@ test('my test', async () => {
   expect(result).toBe('foo');
 });
 ```
+
+#### `onlyFunctionsWithExpectInLoop`
+
+When `true`, this rule will only warn for tests that have `expect` calls within
+a native loop.
+
+```json
+{
+  "rules": {
+    "jest/prefer-expect-assertions": [
+      "warn",
+      { "onlyFunctionsWithAsyncKeyword": true }
+    ]
+  }
+}
+```
+
+Examples of **incorrect** code when `'onlyFunctionsWithExpectInLoop'` is `true`:
+
+```js
+describe('getNumbers', () => {
+  it('only returns numbers that are greater than zero', () => {
+    const numbers = getNumbers();
+
+    for (const number in numbers) {
+      expect(number).toBeGreaterThan(0);
+    }
+  });
+});
+```
+
+Examples of **correct** code when `'onlyFunctionsWithExpectInLoop'` is `true`:
+
+```js
+describe('getNumbers', () => {
+  it('only returns numbers that are greater than zero', () => {
+    expect.hasAssertions();
+
+    const numbers = getNumbers();
+
+    for (const number in numbers) {
+      expect(number).toBeGreaterThan(0);
+    }
+  });
+
+  it('returns more than one number', () => {
+    expect(getNumbers().length).toBeGreaterThan(1);
+  });
+});
+```